| Pb-based Pb(Zr,Ti)O3 piezoelectric ceramics are widely used in medical,automotive,household electronics,aerospace and national defense fields due to their excellent piezoelectric properties.However,a great threat caused by Pb-based ceramics to human beings and environment due to its toxicity.In addition,Due to the demand in the high temperature environment such as fuel spray,exploration,aerospace etc.Therefore,it is particularly important to prepare some lead-free piezoelectric ceramics with high Curie temperature that can substitute for lead-based piezoelectric ceramics.(1-x)BiFeO3-xBaTiO3(BF-BT)piezoelectric ceramics,which have been widely studied by scholars due to their high Curie temperature and better electrostrain,possess broad application prospects in the hightemperature actuators fields.However,due to the volatilization of Bi3+ions and the Fe3+ions reduced during the sintering of BF-BT piezoceramics,it is very difficult to prepare the BF-BT piezoceramics with pure perovskite structure,and they possess inferior strain and large conductivity as well as high driving electric-field.To solve these problems,we adopted elements substitution,component solid solution and second phase recombination to study the effect mechanism of defect,phase structure,domain morphology and grain boundary on strain of BF-BT-based ceramics.The specific results are as follows:Adopting appropriate Fe2+ions substituted for Fe3+ions to restrict Fe3+ions reduced and improved resistivity,and meanwhile,constructed defect dipoles to reduce the energy barrier required for domain switching.Therefore,the 0.7Bi(Fe3+1-xFe2+x)O3-0.3BaTiO3 piezoelectric ceramics were prepared.At x=0.07,excellent comprehensive electrical properties and pure perovskite phase structure were obtained,Smax=0.24%(50 kV/cm),d33*=d33#=480 pm/V,H=13.8%,Tc=485℃.The excellent electric-induced strain and low hysteresis are attributed to the construction of defect dipoles,reducing the friction damping and barrier required for domain switching,and promoting domain growth.Unfortunately,its low resistivity makes it impossible to use in high temperature fields.In terms of the low resistivity in the BF-BT-based ceramics,introducing HfO2 with high band gap into BF-BT piezoceramics to further increase electric-induced strain and resistivity.Hf4+ with large radius substituting for Ti4+with small radius would restrict the movement of B-site ions,and thus improves domain morphology and induces phase transition.Here,the 0.7Bi(Fe3+0.93Fe2+0.07)O3-0.3Ba(Ti1-xHfx)O3 piezoceramics were prepared.At x=0.05,Smax=0.35%(100 kV/cm),d33*=350 pm/V,d33#=250 pm/V,H=40%,Tc=498℃,and the resistivity increased 272%stronger than that of the non-modification composition.The excellent electric-induced strain is attributed to phase transformation under the external electric field and reduction of barrier required for domain switching du to nanodomains embedded into submicron domains.However,its driving electric field too high to meet the needs of practical application.The law between the low driving electric field and superior electric-induced strain are studied,and the(1-x)[0.7Bi(Fe3+0.93Fe2+0.07)O3-0.3Ba(Ti0.95Hf0.05)O3]-x(Sr0.7Bi0.2)TiO3 piezoceramics were prepared.At x=0.03,the superior electric properties were obtained,Smax=0.24%,d33*=396 pm/V,d33#=304 pm/V,H=30.2%,Tc=439℃.Within 25～245℃,electric-induced strain takes on increasing trend,the maximum strain variation rate and hysteresis are 23.7%and 30.2%,respectively.The superior electric-induced strain properties are attributed to the formation of polar nanoregions;however,the dynamic temperature Tf(242.7℃)of polar nanoregions is much higher than room temperature,resulting in inferior electric-induced strain at room temperature.The compositions with ergodic polar nanoregions at room temperature and superior electricinduced strain were successfully designed,the(1-x)[0.7Bi(Fe3+0.93Fe2+0.07)O30.3Ba(Ti0.95Hf0.05)O3]-x(La0.1Sr0.8)TiO3-δ piezoelectric ceramics were prepared.Introducing relaxor with composition disorder at A-site into ferroelectric to weaken long-range ferroelectric order,increasing the contents of polar nanoregions and decrease the dynamic temperature Tf to room temperature.At x=0.03,Tf=25.7℃,the superior electric-induced strain properties were obtained,Smax=0.32%(60kV/cm),d33*=533 pm/V,d33#=376 pm/V,H=50.1%,Tc=435℃.At the range of 25 to 245℃,the maximum strain variation rate and hysteresis are 31%and 50.1%,respectively.To further reduce driving electric field and improve electric-induced strain performance at room temperature.xBa(Sn0.11Ti0.89)O3/0.97[0.7Bi(Fe3+0.93Fe2+0.07)O3-0.3Ba(Ti0.95Hf0.05)O3]0.03(La0.1Sr0.8)TiO3-δ 0-3 composite piezoceramics were prepared.Utilizing the strain coupling and polarization coupling effect to reduce the driving electric field,and thus the excellent electric-induced strain properties were obtained at low electric field.At 30 kV/cm,at x=5 wt.%,Smax(0.137%),d33*(457 pm/V),and d33#(400 pm/V)in the 0-3 composite ceramics are 161%,162%and 215%higher than Smax(0.084%),d33*(280 pm/V)and d33#(186 pm/V)in the non-composite ceramics,respectively.The H(30%)and Srem(0.017%)in the 03 composite ceramics are 230%and 165%lower than H(69%)and Srem(0.028%)in the noncomposite ceramics. |
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